FIGS. 1A, 1B and 1C (left-hand side view, right-hand side view and top view respectively) illustrate an example of an automated storage/retrieval system according to the prior art.
In this example, the system comprises a storage unit E1 comprising two racks 12L and 12R, with superimposed levels (14L and 14R) and sub-divided into locations (double depth in this example) each intended to receive two loads P.
The storage unit E1 also comprises an exit buffer station 18L and an entry buffer station 18R. The exit buffer station 18L is positioned at one end of the rack 12L and is adjacent to it. It is constituted by a set of exit buffer conveyors 20L. The number of exit buffer containers 20L is the same as that of the levels 14L in the rack 12L. The entry buffer station 18R is positioned at one end of the rack 12R, and is adjacent to it. It is constituted by a step of entry buffer conveyors 20R. The number of entry buffer conveyors 20R is the same as that of the levels 14R in the rack 12R. The buffer conveyors 20R and 20L are for example of a motor-driven type with a dual sense of rotation.
A lane serves the two racks 12R and 12L and comprises at each level a channel for moving. Shuttles 16 (for example one per level, of a motor-driven and single-load or multi-load type) make it possible, by moving on the channels to transfer loads between the locations (within the racks 12R and 12L) and the buffer conveyors 20R, 20L. Each shuttle 16 of a given level has access to locations (within the racks 12R and 12L) and the buffer conveyors 20R and 20L of this given level.
In order to facilitate the description, we consider the axis (referenced A in FIG. 1C) of the lane between the two racks 12R and 12L and the term “right-hand part of the system” (referenced D in FIG. 1C) and “left-hand part of the system (referenced G in FIG. 1C) designate the two parts of the system located on either side of this axis A. It will be noted that the “side view of the right-hand part” presented in FIG. 1B and the “side view of the left-hand part” presented in FIG. 1A are both views along a same direction (referenced 10 in FIG. 1C). This observation is valid for all the side views of the right-hand and left-hand parts presented here below.
The system also comprises two elevators 22R and 22L. Each elevator is positioned at the end of the buffer conveyors 20R and 20L situated at the end of one of the racks 12R and 12L. Each elevator has a single level used to transport a load delivered by one of the buffer conveyors 20L and 20R. In a first known variant (not shown), each elevator has a single level used to transfer two loads. In a second known variant (not shown), each elevator has two superimposed levels each used to transport two loads (giving a total capacity of four loads).
Each elevator 22R and 22L marks a controlled stop facing each buffer conveyor 20R and 20L. These stops are used to obtain entries/exits of loads onto the racks 12R and 12L.
Each elevator is positioned between firstly the buffer conveyors 20R and 20L situated at the end of one of the racks 12R and 12L and secondly interface conveyors for the entries/exits of loads into/out of the system. In the example illustrated, the elevator 22R of the right-hand part of the system is associated with two entry interface conveyors 70R and 80R forming an entry interface station 90R (see FIG. 1B), and the elevator 22L of the left-hand part of the system is associated with two exit interface conveyors 70L and 80L forming an exit interface station 90L (see FIG. 1A). In other words, each elevator 22R and 22L enables a transfer of loads between: on the one hand the buffer conveyors 20R and 20L at the end of the one of the racks 12R and 12L, and on the other hand the entry interface conveyors 70R and 80R and the exit interface conveyors 70L and 80L.
The entry interface conveyors 70R and 80R, the elevator 22R and the buffer conveyors 20R (i.e. the right-hand part elements) as well as the shuttles 16 (common to the right-hand and left-hand parts) enter the loads onto the two racks 12R and 12L. The exit interface conveyors 70L and 80L, the elevator 22L and the buffer conveyors 20L (i.e. the elements of the left-hand part) as well as the shuttles 6 (common to the right-hand and left-hand parts) obtain the exit of the loads out of the two racks 12R and 12L. The shuttles have access to the locations of the rack 12R of the right-hand part as well as to the locations of the rack 12L of the left-hand part.
A control system (symbolized by the rectangle referenced 95) controls at least certain of the elements of the storage unit E1 (for example the buffer conveyors and the shuttles) the elevators 22R and 22L and the entry interface conveyors 70R and 80R and exit interface conveyors 70L and 80L.
One drawback of such a system of storage and retrieval according to the prior art is that the cycle time of each elevator proves to be relatively great compared with the number of actions of entry or exit performed. Indeed, at each action of entry or exit of a load, a half cycle is “lost” in the movement of the elevator in an empty state and does not consist of a value-adding action
Neither the above-mentioned first known variant (each elevator has a single level to convey two loads) nor the second known variant (each elevator has two superimposed levels each enabling the transportation of two loads) enables this drawback to be overcome.
More generally, one of the problems encountered in the designing of automated storage/retrieval systems is that of optimizing the implementation of each of the elements constituting the system and especially of the elevators and of optimizing the general pace of the system making it possible for example to achieve an objective in terms of preparing orders (i.e. a number of loads made available to prepare a set of orders in a given time).
Another set of problems is related to the capacity to be able to deliver the loads in a desired order when they exit from the system. This set of problems is known as the “sequencing constraint”.